This invention relates to nozzles for dispensing gasoline into vehicle fuel tanks and more specifically to systems for controlling the operation of a dispensing nozzle having a vapor receiving system.
Current environmental regulations require in some areas that gasoline vapors displaced from a vehicle fuel tank while being filled are to be recovered in order to prevent their escape into the atmosphere. One method of complying with this requirement is to have a closed filling system wherein the vapors displaced from the fuel tank are forced back into the underground hydrocarbon storage tanks. Many systems have been designed to recover vapors by this direct displacement method. Most of them include a vapor receiving system surrounding the discharge spout of the nozzle which has a sealing face for making a tight seal against the fillpipe opening and an outlet which is connected to the underground tanks so that the vapors are displaced into the vapor receiving system and back through the vapor return line to the underground tanks. A second system for collecting the vapors is a vacuum assist system which utilizes a vacuum pump in the vapor return line to assist the flow of vapors into the underground tank or other collection facility.
One problem that has arisen in the use of these vapor receiving systems is that once the vehicle fuel tank becomes filled, the dispensing nozzle automatically shuts itself off, the operator often tries to fill the tank further. These attempts may result in gasoline being pumped back into the vapor receiving system and back to the background tanks through the vapor return line. This recycling of the gasoline can result in the customer buying more gasoline than he has actually received and maybe even more than the tank in his vehicle can hold. In addition, leakage of gasoline out through the seal of the vapor receiving system with the fillpipe can increase the risk of fire. Another problem is that the efficiency of vapor recovery is decreased if liquid gasoline is in the vapor return line.
Understanding the reason behind this problem requires an understanding of the operation of the automatic shut-off system used in most nozzles commercially available today. The shut-off system utilizes the pressure differential between two pressure chambers to create a differential displacement of a flexible diaphragm separating the two chambers. The position of this diaphragm determines whether or not the actuating lever which is moved to open the main valve of the nozzle, is able to actuate the main valve. In operation, when the pressure in a first chamber falls below a predetermined level, the diaphragm displacement disables the actuating lever so that it can no longer open the main nozzle valve.
The reduced pressure in the first chamber is achieved by having it connected to a vacuum source such as a venturi arrangement in which the vacuum is created by the flow of gasoline through the venturi. As is known by those skilled in the art, this vacuum is relieved through a vent line connected to this first chamber at one end and at the end of the discharge spout at the other end. When the liquid level reaches the end of the spout, the vent tube outlet is covered and the vacuum caused by the venturi cannot be relieved, so the diaphragm is displaced to cause the main valve to close.
However, if the operator desires, he can attempt dispensing of gasoline again since the diaphragm returned back to its normal position when the flow of gasoline stopped because the automatic shut-off system has an inherent time delay before disabling the nozzle again due to the fact that the required vacuum force from the flow of gasoline through the venturi must be created again. Thus, the operator can initiate gasoline dispensing ad infinitum, causing a certain amount of gasoline to be pumped into the tank each time.
When using a vapor receiving system with the dispensing nozzle, the operator cannot visually ascertain the liquid level in the tank. Therefore, with further attempts to "top off" the tank, a point is reached where gasoline is pumped into the vapor receiving system.